Working with mice, Johns Hopkins researchers have solved a key part of a muscle regeneration mystery plaguing scientists for years, adding strong support to the theory that muscle mass can be built without a complete, fully functional supply of muscle stem cells. "This is good news for those with muscular dystrophy and other muscle wasting disorders that involve diminished stem cell function," says Se-Jin Lee, M.D., Ph.D., lead author of a report on the research in the August issue of the Proceedings of the National Academy of Sciences, and professor of molecular biology and genetics at the Johns Hopkins University School of Medicine.